Medication Oversupply and Outcomes in Patients with Diabetes Abstract Effective management of diabetes often requires patients to follow complex, multiple-drug regimens to control blood glucose, blood pressure, and lipids. However, these regimens are difficult for patients to follow and come with increased risk of adverse drug events, particularly for older adults or those with other serious co- morbidities. Although the dangers of diabetes patients'obtaining less medication than prescribed (i.e. medication undersupply) are well-recognized, the risks of obtaining oversupply of medications - greater than 120% of the medication required for maintaining adherence - have been far less appreciated. If having large quantities of unneeded medication on hand promotes patients'overuse or misuse of medications, then negative outcomes may result. A few studies conducted in "closed" health systems in which providers and pharmacies are connected through a single electronic health record (EHR) have found oversupply of medications used in diabetes to be costly and common, occurring in up to 50% of patients, but the magnitude and risk factors of oversupply for diabetes patients in a typical U.S. practice is unknown. It is also unknown the extent to which oversupply may pose a safety risk to patients with diabetes, particularly those with greater clinical complexity who may have difficulty managing and tolerating prescribed medications. The proposed research addresses these critical questions by 1) describing the prevalence and risk profile of oversupply of oral hypoglycemic, antihypertensive, and dyslipidemic medications in diabetes patients, and 2) examining the effect of oversupply on all-cause and possible drug-related short-term negative outcomes (hospitalization, emergency department use, or death) and whether these effects are greater for more versus less complex patients. Our sample includes approximately 2,440 patients with diabetes who were cared for by a large Midwestern multi-specialty physician group during 2006-2008. Our approach utilizes a unique data resource linking electronic health record data to administrative data from Medicare and a large local health maintenance organization (HMO). We will estimate effects of oversupply on negative outcomes using lagged logistic regression incorporating propensity scores to adjust for several potential sources of confounding. This study will help define the scope, causes, and consequences of medication oversupply in diabetes and lay the groundwork for enhancing medication management interventions and reducing adverse drug events in diabetes patients. PUBLIC HEALTH RELEVANCE: We propose to examine the predictors and consequences of medication oversupply - acquiring more medication than is needed to maintain adherence - for adult patients with diabetes. Oversupply of diabetes medications may lead patients to make errors in following their treatment regimen and result in negative outcomes, but the health risks to patients remain undefined. The results from our investigation will define the scope of an under-recognized patient safety risk in diabetes and inform the design of efforts to improve medication management and reduce adverse drug events in this common, costly, and difficult to manage illness.